1. Field of the Invention
The present invention relates to a circuit for generating clock signals for measuring occurrence times of different events.
2. Description of the Related Art
When the occurrence times of a plurality of events are to be measured, it is known to use a sensor array formed of a plurality of sensors, the outputs of which represent response times. In such a case, it is known to arrange a plurality of timer circuits for respectively measuring the outputs of the sensors, based on a reference frequency.
FIG. 1 is a block diagram of such a known sensor array time measuring system 1. AND gates 3a through 3n and counters 4a through 4n are provided to measure the period of time required for each of the outputs of photosensors 2a through 2n to reach a predetermined level. For example, if the output of photosensor 2a changes from a high (H) level to a low (L) level when a desired response is sensed, the counter 4a counts the number of clock signals generated before the output of photosensor 2a falls from the high (H) level to the low (L) level. Thus, the response times of photosensors 2a-2n correspond to the count values of counters 4a-4n.
With some modifications, the sensor array time measuring system 1 can be adapted to measure the time elapsed before the onset of a particular event. However, in conventional systems for measuring the onset times of events, the number of hardware elements required increases with the number of different events to be measured and with the length of time to be measured. In particular, a large amount of circuitry is necessary where the system must be capable of measuring a wide range of response times.
When the outputs of the sensors of known systems are quantized, it may be unnecessary to measure the response times precisely. Instead, it may be sufficient to obtain data with a degree of precision sufficient to be significant for the sensor array. If the measurement results are to be used in data processing, and if the number of sampling data is unnecessarily large, the succeeding data processing operation requires processing of insignificant data which makes it impossible to obtain data efficiently.
Accordingly, an object of the present invention is to provide a clock signal generating circuit for effectively and efficiently measuring occurrence times of a plurality of events using a relatively small amount of hardware.